Rework how config vars are sourced

- ensure we source config/functions from the correct directory
- move config sourcing up before DOKKU_TRACE to reduce trace output

install

@@ -1,6 +1,6 @@
 #!/usr/bin/env bash
+source "$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)/config"
 set -eo pipefail; [[ $DOKKU_TRACE ]] && set -x
-source "$(dirname "$0")/config"
 
 if ! docker images | grep -e "^$PLUGIN_IMAGE " | grep -q "$PLUGIN_IMAGE_VERSION" ; then
   docker pull "$PLUGIN_IMAGE:$PLUGIN_IMAGE_VERSION"